Purse string sutures are frequently used in surgical procedures to close a tubular section of tissue, e.g., intestinal tissue. Purse string sutures are also used in the performance of cardiac surgery wherein the heart, major arteries, and/or major veins are cannulated for cardiopulmonary bypass (CPB). More specifically, a purse string suture is used to seal the tissue around a cannula placed within the cardiac tissue.
Cardiopulmonary bypass requires a cannula (or cannulae) to be placed into the right side of the heart (typically the right atrium) or in the major veins (typically the superior vena cava and/or inferior vena cava) to drain blood from the patient and deliver it to a pump-oxygenator, commonly known as the heart-lung machine. In the pump-oxygenator, the blood is exposed to a gaseous mixture that eliminates carbon dioxide and adds oxygen to the blood. The oxygenated blood is then returned to the body through a perfusion cannula. In some circumstances, the perfusion cannula is placed into a large peripheral artery, such as the common femoral artery. However, because of a higher incidence of complications associated with that method of blood return to the body, it is more acceptable to return the blood through a cannula placed directly into the ascending aorta.
The insertion of the arterial (aortic) perfusion and the venous drainage cannula are usually performed in the following fashion. After the patient's chest has been opened and the pericardium (the protective sac around the heart) has been entered, two concentric purse string sutures are placed into the anterior wall of the ascending aorta just proximal to upstream of the brachiocephalic trunk. The diameter of the purse string suture is made large enough to accommodate the size of the aortic perfusion cannula. A "choker" tube or sleeve is positioned over the trailing ends of the suture threads to act as a tourniquet for tightening the purse string suture. A small incision is then made through the wall of the aorta into its lumen in the center of the purse-string sutures. The aortic perfusion cannula is then inserted through that incision into the aorta to prevent the escape of blood prior to connection to the pump-oxygenator. The purse string sutures are then tightened by means of their respective tourniquets to seal the aortic wall around the perfusion cannula in order to prevent the escape of blood from the aorta. Air is then evacuated from the perfusion cannula as it is joined by a connector to the tubing from the pump-oxygenator. A cross-clamp is placed on the aorta just downstream of the aortic root and upstream of the cannula to ensure that no blood flows back into the aorta during CPB.
The venous drainage cannula(e) is similarly inserted directly through an incision centered within a single purse-string suture into the right atrium of the heart or into the superior and/or inferior vena cavae for connection to the drainage side of the pump-oxygenator. The respective purse string sutures are tightened by means of a tourniquet as described above. An external clamp is sometimes placed around the vena cava to prevent blood from flowing between the vessel lumen and the venous cannula.
Cardiopulmonary bypass is instituted by allowing unoxygenated blood which is returning to the right side of the heart to be diverted into the pump-oxygenator where it is oxygenated and temperature-adjusted. From there, the blood is pumped into the patient's arterial system via the aortic perfusion cannula.
When it is desired to arrest cardiac function, a cardioplegic solution, such as potassium (KCl) is delivered to the myocardium by one or a combination of two general techniques, antigrade and retrograde. The infusion of cardioplegia fluid in an antegrade manner is accomplished by means of a cardioplegia cannula inserted at the aortic root wherein the fluid flows in the normal direction into the coronary ostia through the coronary arteries and into capillaries within the myocardium. Retrograde infusion of cardioplegia solution is directed into the right coronary sinus by means of a cardioplegia cannula inserted in the right atrium, and flows backwards into the coronary arteries and capillaries of the myocardium. With both techniques, a purse string suture may be used to seal the tissue around the cannula.
Typically, two concentric rows, with off-setting or staggered stitches and with each row having 4 to 5 stitches, are placed for the arterial perfusion cannula. Because the blood flow pressure is greater on the arterial side of the heart, a double purse string suture is used as a precaution in case one suture breaks. Two rows of stitches also help to minimizes the risk of blood leakage from the incision site. On the other hand, because there are not the pressure concerns on the venous side, only a single purse string suture having about 5 to 6 stitches is typically used for venous cannulation. As the cardioplegia camula is in a portion of the circulatory system that has been bypassed by CPB, there is virtually no concern of blood leakage, and only a single purse string suture is necessary to seal the tissue around the cannula and hold it in place.
The diameter of a purse string sutures is sized to accommodate the respective cannulae. Arterial cannulae range in size from about 8 French, having an inner diameter of about 0.10 inch or 2.5 mm (for pediatric use to) about 24 French, having an inner diameter of about 0.30 inch or 8.0 mm. Accordingly, the inner purse string suture for an arterial cannula has a diameter which is preferably slightly larger (about 3.2 mm or 1/8 inch) than that of the cannula, and the outer suture has a diameter which is also about 3.2 mm or 1/8 inch greater than the inner suture. As venous cannulae tend to be slightly larger than arterial cannulae to compensate for the slower flow of blood, their sizes typically range from about 12 French, having an inner diameter of about 0.15 inch or 4.0 mm, to about 40 French, having a diameter of about 0.52 inch or 13.2 mm. The diameter of the associated single purse string suture is then preferably about slightly larger (about 3.2 mm or 1/8 inch) than that of the venous cannula.
Conventionally, purse string sutures are manually stitched by the surgeon. In laparoscopic surgery, for example, where tubular ends of tissue are being tied off, the entire thickness of the tissue wall may be penetrated to achieve the desired suturing. However, in cardiac surgery, and particularly in the context of aortic cannulation, total penetration of the aortic wall by the purse string suture can cause catastrophic effects such as blood leakage, the introduction of air into the arterial system, and the disruption of calcified deposits from the innermost layer of the aortic wall. Additionally, penetration of the aortic wall by a needle or suture can damage the endothelial layer increasing the likelihood of the long-term buildup of stenotic deposits within the aorta. Thus, the surgeon must be cautious so as not to penetrate the entire thickness of the vessel wall. Uniform placement, spacing and length of the stitches are also important to minimize the risk that some of the stitches may rip away from the tissue when the ends of the purse string suture are pulled. With manual stitching, it is difficult to obtain uniform and accurate penetration of the purse string suture into the tissue. It is also difficult for a surgeon of average skill to obtain stitches which are uniform in length and evenly spaced apart.
Another drawback of applying purse string sutures manually is the space required in the surgical opening for the surgeon's hands. With the progression towards less invasive cardiac surgical techniques which permit the visualization and manipulation of surgical instruments through less invasive openings in the chest, there is a need for a compact surgical instrument which automatically places purse string sutures in tissue structures and obviates the need for space to view the stitching procedure and accommodate the surgeon's hands.
Another objective of less invasive surgeries is to reduce the time a patient is subjected to potentially traumatic procedures, such as the necessary clamping of the aorta prior to implementing CPB and thereby reduce the interruption in systemic circulation. Although some cardiac surgeon's are very skilled and adept at placing purse string sutures by hand, it takes about 3 to 5 minutes to apply each purse string suture. A total of 3 to 5 purse string sutures being placed for the entire cannulation procedure, manual stitching adds considerable time to the entire procedure.
There are several surgical instruments for applying purse string sutures about the periphery of tubular tissue without the need for a surgeon to manually insert the suture needles into the tissue. For example, U.S. Pat. Nos. 4,915,107, and 5,188,636 disclose instruments in the form of a pair of serrated tissue clamping jaws provided with teeth. Needle passages extend through the teeth on each jaw for receiving a needle attached to a suture to be threaded through the tissue. The tissue clamping jaws act to gather tissue into the spaces between the teeth and then the needles are advanced through the needle passages. Other instruments are disclosed, in U.S. Pat. Nos. 4,749,114, 4,821,939, 5,242,457 and 5,484,451 for example, which utilize a plurality of staples for applying purse string sutures to human tissue. U.S. Pat. No. 5,484,451 discloses a surgical stapler having a pair of jaws with each jaw containing a staple cartridge for holding staples. The staples are shaped to have an eyelet for receiving a purse string suture.
These aforementioned devices are adapted for the application of a purse string suture circumferentially about an end or the periphery of a tubular tissue structure. They are not practical for applying purse string sutures to a closed vessel or vessel lumen, such as the heart or aorta, where it is desirable to apply a suture to only one wall or side of the vessel or lumen rather than about its periphery. The clamping jaw mechanism of these devices is also undesirable for use in creating purse string sutures in cardiac tissue, and the aorta in particular, as they tend to be traumatic to the tissue, increasing the risk of embolism. Furthermore, these instruments are not suitable for applying a purse string suture where it is necessary to avoid penetrating the suture through the entire thickness of the tissue wall, such as in the aorta, or where the use of staples to secure a suture is less than desirable due to the increased risk of thrombosis and embolisms associated with stapling vascular tissue.
Accordingly, a general objective of the present invention is to provide a device and a method for automatically applying a purse string suture to a single wall of a vessel or vessel lumen which does so more accurately and in less time than manual suturing.
Another objective of the present invention is to provide an instrument for a traumatically providing a purse string suture which does not employ clamping jaws or staples.
It is also an objective of the present invention to provide a device which automatically applies a purse string suture to a tissue wall where the suture penetrates through less than the full thickness of the wall.
It is also an objective of the present invention to provide a surgical instrument for automatically applying a purse string suture to cardiac tissue which can be inserted through a relatively small opening in the chest, which does not necessitate viewing of the suturing site for achieving accurate results, and which occupies minimal space in the surgical opening.
Another object of the present invention is to provide an automatic purse string suture instrument which incorporates a cutting or puncturing element to incise the area within a purse string suture for placement of a cannula or cannulae.
Yet another object of the present invention is to provide an apparatus which applies two concentric purse string sutures simultaneously.
These and other objectives and advantages of the present invention will be more fully understood and appreciated by reference to the drawings and the following description of the invention.